CELL PENETRATION BY ACIDS. 
IV. NOTE ON THE PENETRATION OF PHOSPHORIC ACID. 
By W. J. CROZIER. 
Contributions from the Bermuda Biological Station for Research, No. 83. 
(Received for publication, December 12, 1917.) 
: 
I. Measurements of the relative speeds with which acids penetrate 
protoplasm, as carried out by different observers upon widely different 
tissues containing natural indicators, have shown in general a noteworthy 
agreement with regard to the way in which the various acids are arranged 
in order of their penetrating ability (Harvey, 1914; Crozier, 1916, a, 6; 
Haas, 1916, a). This must indicate some fundamental fact about the or- 
ganization of protoplasm, since some of the relations observed are such 
as might not be predicted. It is, then, of interest to examine an instance 
in which minor disagreement has been found. The agreement referred to 
obtains in acid solutions which are 0.01 N by titration, and it has been 
shown (Crozier, 1916, a, 6) that, owing to the several forms of the penetra- 
tion curves, the sequence of increasing penetrating ability may vary with 
the concentration at which the comparisons are made; and it was pointed 
out that a similar condition obtained with regard to comparisons at any 
one hydrogen ion concentration. Any special influence affecting the de- 
termination of the change of indicator by a particular acid may cause the 
form of its penetration curve to be different with different tissues, accord- 
ing to the variation of this special factor. Thus, among other possibili- 
ties, variations in the composition of the surface layer of the cell, or in the 
‘buffer’? conditions under which the intracellular titration fakes place, or 
variations in the behavior of the different indicators used, might be ap- 
pealed to to explain observed differences in the relative order of penetra- 
tion for different tissues; and it might be expected.that an acid whose salts 
have special significance in connection with protoplasm would be one to 
show characteristic variations from cell to cell. 
Now, Haas (1916, a) found that for one kind of plant material used in his 
experiments, the petals of Browallia, phosphoric acid produced the color 
change signifying penetration more rapidly, at 0.01 nN H™ concentration, 
than did oxalic, tartaric, lactic, citric, or acetic acids; whereas, with the 
perianth cells of a hyacinth, this took place more slowly than in oxalic 
acid. Harvey (1914) observed the penetration of phosphoric acid, at this 
concentration, to occur with about the same speed as malonic or tartaric, 
bus more slowly than with lactic or oxalic. 
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